1. Field of the Invention
The present invention relates to devices used to clean tanks and other containers, including but not limited to storage tanks, marine vessels, and similar equipment. The invention is more particularly suited to cleaning the interior surfaces of such tanks using multiple spraying devices installed on repositionable mounts within the tank.
2. Description of Related Art
Tanks, containers and other similar enclosures are commonly used to store liquids in any number of different applications. Tanks of varying sizes and shapes are frequently used to store liquids in connection with numerous industries including, but not necessarily limited to, the oil and gas industry. Such tanks are especially prevalent in the offshore oil and gas industry, in particular, where they are often used to store different types of fluids on boats and drilling rigs.
In many cases, tanks on boats and drilling rigs are used to store and transport drilling fluids. Such drilling fluids often contain chemicals and other additives designed to adjust or control certain characteristics of the fluids. Common drilling fluid additives include gelling agents (e.g., colloidal solids or emulsified liquids), weighting materials (e.g., barite or bentonite, etc.), and other chemicals which are used to maintain fluid properties within desired parameters. Further, although drilling fluids have historically been water-based, improved results have been obtained using oil-based or synthetic-based drilling fluids, especially in severe drilling environments. Many of these additives, as well as oil-based and synthetic-based drilling fluids, can be harmful to personnel and the environment.
Different stages of the drilling process may require different types of drilling fluids having different characteristics. In such cases, the limited tank capacity of boats and drilling rigs necessitates using the same tanks to store such different drilling fluids. However, because such different types of drilling fluids may not be compatible with one another, it is frequently necessary to clean such tanks before switching the fluids to be stored in such tanks.
The process of cleaning tanks can often prove to be difficult, expensive and time consuming. Such cleaning can be especially challenging when solids are permitted to drop out of suspension. In such cases, solids are often deposited in the tanks, forming hardened layers at or near the bottom of such tanks that cannot be simply drained from the tanks. Frequently, such deposited solids must be removed before interior surfaces of the tanks can be cleaned.
Personnel are often utilized to manually clean storage tanks on boats and drilling rigs. In such cases, personnel are required to physically climb inside the tanks and use suction hoses, hand-held pressure washers, shovels, and other tools to clean the interior surfaces of the tank. This is a highly labor intensive endeavor, particularly when hardened deposits of solids are present, and when such personnel are required to wear suitable protective equipment. The difficulty of such work is often exacerbated on hot days when temperatures inside the tanks can be uncomfortably high with poor ventilation. Further, this method of cleaning tanks raises safety concerns, because personnel inside the tanks are frequently exposed to drilling fluid residue, toxins and contaminants that may be present within such tanks.
Various automated tank cleaning devices have been developed in an attempt to eliminate the numerous problems associated with manual cleaning of tanks, such as tanks located on boats and drilling rigs. However, performance of such prior art cleaning devices has proven to be less than satisfactory, often because such prior art cleaning devices cannot adequately reach all areas of tanks to be cleaned. Furthermore, most chemical compounds used in connection with prior art automated cleaning devices are ineffective at removing solids from tanks being cleaned. Moreover, prior art devices can be cumbersome, as well as difficult and expensive to operate.
One automated technique for cleaning storage tanks utilizes a programmable pressure washer that can be permanently mounted to the tank shell, or inserted through a permanently installed fitting. These systems usually include a rotating washer head that is provided with one or more nozzles that are moved automatically to make the wash head cover a specified area. These pressure washers are normally adapted to be installed in a fixed position relative to the tank with the wash head providing all the movement required.
In general, the tank geometry, including any internal obstructions, and the distribution of deposits make it difficult to match the washing pattern of a single washing head to a specific tank configuration because with the types of washing systems described above, some areas are more intensely washed than others. Further, so-called “shadow” areas that are shielded from the direct impact of the jet by pipe, stanchions, baffles and the like, are not well cleaned. Therefore, many of the systems described above employ several washing heads simultaneously and may operate for extended periods of time, such that excess consumption of washing liquid may occur. This excess consumption of washing liquid represents a poor exploitation of time, an increased energy cost, possibly an undesired wear on the tank interior, and it involves an increased cost of purifying the waste liquid which is discharged in larger quantities than may be necessary. Further, in many cases, access is limited to a manway or other large openings in the tank, and nozzles positioned only at these locations cannot completely clean tanks with shadowed areas.
Accordingly, there is a need for an efficient and effective automated system for cleaning tanks and similar enclosures, including tanks containing solids-laden fluids and hardened deposits of solids. Such system should permit cleaning of entire tanks or other enclosures, and should minimize the need for personnel to physically enter such tanks or other enclosures by employing multiple repositionable spraying devices to be employed at several locations within the tank. It is believed that the apparatus and method described and claimed herein directly address these needs.